1. Field of the Invention
This invention relates to a bellows-shaped joint boot mainly used for tripod type constant velocity joints or the like of automobiles.
2. Description of Related Art
As one of constant velocity joints for use in a driveshaft, etc. of vehicles, a tripod type joint is well known.
A tripod type constant velocity joint is, as shown in FIGS. 7, 8 by way of example, comprised of a tripod 4 wherein three trunnions 3 having respective rollers 2 are provided at the one shaft 1 of input and output side shafts in a manner projecting in a normal direction to the axis thereof, and an outer housing 6 provided at an end of the other shaft 5. The outer housing 6 has on its inner periphery three axial grooves 6a for sliding corresponding to the tripod 4. The constant velocity joint is constructed so that the rollers 2 of the tripod 4 are fitted to be axially slidable in the sliding grooves 6a, thereby enabling the transmission of running torque while enabling the angulation of both shafts 1, 5.
In such constant velocity joints, in order to prevent the ingress of dust and extraneous substances into the joint or to retain the grease sealed therein, it is a common practice to equip a bellows-shaped joint boot 100 capable of appropriate expansion and contraction and bending deformation so as to cover the shaft 1 on the tripod 4 side from the outer housing 6. The joint boot 100 is constructed so that its axially one end is formed as a large-diameter attachment part 101 which is fitted in the outer periphery of the outer housing 6 and fixed by means of a tightening member 7 such as a ring-like band and its other end is formed as a small-diameter attachment part 102 which is fixed on the outer periphery of the shaft 1 on the tripod 4 side by means of a tightening member 8 such as ring-like band, and the both 101, 102 are integrally joined by a bellows part 103.
As shown in FIG. 8, the outer housing 6 is provided, on its external periphery, with three circumferentially equidistantly disposed recessed portions 6b, corresponding to the disposition of the sliding grooves 6a on its internal periphery and hence, the external peripheral contour of the outer housing 6 is of a non-circular shape assuming a circumferentially sinusoidal (salient and reentrant) form. Because of that, the large-diameter attachment part 101 of the joint boot to be attached to the outer housing 6 has an internal peripheral contour assuming a non-circular shape conforming to the external peripheral contour of the outer housing 6. Stated another way, the internal periphery of the large-diameter attachment part 101 is formed to bulge inwardly in a raised fashion in circumferentially three places thereof, corresponding to the recessed portions 6b of the outer housing 6.
Where such inwardly bulging portions 104 of the large-diameter attachment part 101 are formed as solid thick-walled portions as illustrated in FIG. 7, the thick-walled portions and thin-walled portions are formed alternately in the circumferential direction of the large-diameter attachment part 101, and consequently, a problem arose in that sufficient sealing properties to the outer housing 6 were difficult to ensure. To solve such problems as this, Patent Reference 1 listed below discloses an example, wherein the inwardly bulging portions of the large-diameter attachment part are constructed each of an inner wall portion jutting inwardly in a curved form, an outer wall portion in an arc form on the outer periphery side, and a plurality of strut walls linking the inner wall portion and outer wall portion, the strut walls being disposed equidistantly in the circumferential direction and extending parallel with one another. Another example is disclosed in Patent Reference 2 listed below, wherein the inner wall portion and the outer wall portion are linked by a single strut wall in circumferential centers of both.
[Patent Reference 1] EP 0 915 264A2, A3
[Patent Reference 2] JP-A-2003-329057
Where the inner wall portion and the outer wall portion are linked by a plurality of mutually parallel strut walls disposed equidistantly, as is the technology disclosed in the foregoing Patent Reference 1, in the circumferentially central part of the bulging portion, it is possible to ensure a large cross-sectional area of relief holes, which are a hollow part formed between two strut walls, whereas in circumferential ends of the bulging portion, the cross-sectional area of relief holes is smaller. For that reason, cores for molding such small relief holes are difficult to demold, so that the problem is encountered that the moldability is impaired.
On the other hand, where the inner wall portion and the outer wall portion are linked by a single strut wall in the circumferential centers of both, as is the technology disclosed in Patent Reference 2 above, the moldability is good, but there is still the problem that the contact pressure the inner wall portions exert on the outer housing when tightening and fixing the large-diameter attachment part is difficult to be equalized in the circumferential direction.